1. Field of the Invention
The present invention relates to an eye axis detector for specifying the watching point of a user or photographer with a still camera, a video camera and so on having the eye axis detector. This case is concerned with the improvement of U.S. Ser. No. 586,228 by the present assignee.
2.Related Background Art
Conventionally, various so-called eye axis detectors have been proposed to determine which position on the observation plane the user (photographer) is watching.
For example, in Japanese Laid-Open Patent Application No. 61-172552, the eye axis (watching point) is obtained by projecting the light flux from a light source onto an anterior portion of the eye to be tested and using a cornea reflected image based on the reflected light from a cornea and an imaging state at the central position of pupil.
FIG. 8 is an explanation view showing a principle of an eye axis detection method proposed in the same application.
In FIG. 8, 704 is a light source such as a light emitting diode for radiating the infrared ray insensible to the observer, which is disposed at a focal plane of a projector lens 706.
The infrared ray emitted from the light source 704 is converged by the projector lens 706, reflected at a half mirror 710, and illuminates a cornea 701 in a bulb 702 of the eye 700. A part of the infrared ray reflected from a surface of the cornea 701 transmits through the half mirror 710 and is focused by a light reception lens 707 to form an image at a position d' on an image sensor 709.
The light flux from end portions a, b of an iris 703 is led via the half mirror 710 and the light reception lens 707 onto the image sensor 709, at positions a', b' of which are formed images of the end portions a, b. When the rotation angle .theta. of an optical axis B for the bulb of the eye with respect to an optical axis A of the light reception lens 707 is small, the coordinate Zc at a central position c of the iris 703 can be represented by EQU Zc.congruent.(Za+Zb)/2
providing that Z coordinates at end portions a, b of the iris 703 are Za, Zb.
Also, providing that the Z coordinate at an occurrence position d of a cornea reflected image (primary Purkinje image) is Zd, and the distance from a center of curvature 0 for the cornea 701 to a center C of the iris 703 is OC, the rotation angle .theta. of the optical axis B for the bulb of the eye substantially satisfies the expression EQU OC.multidot.sin.theta..congruent.Zc-Zd (1)
Hence, by detecting a position of each singular point (the occurrence position d of cornea reflected image and images Zd', Za', Zb' of end portions a, b for the iris on the image sensor 709), the rotation angle .theta. of the optical axis B for the bulb of eye, and thus the eye axis of the subject can be obtained. Then, the expression (1) can be rewritten as EQU .beta..multidot.OC.multidot.sin.theta..congruent.(Za'+Zb')/2-Zd'(2)
Where .beta. is a magnification determined by the distance l between the occurrence position d of cornea reflected image and the light reception lens 707, and the distance l.sub.0 between the light reception lens 707 and the image sensor 709, which is usually almost constant.
In this way, by detecting the direction of eye axis (watching point) for a tested eye of the observer, it can be known which position on a focal plane the photographer observes in a single lens reflex camera, for example.
This is effective in the automatic focus detector, for example, such that where the range finding point is provided not only at a center of picture but also at plural locations within the picture, the automatic focus detection can be performed by selecting the range finding point automatically in such a way as to consider the point at which the observer looks as the range finding point while omitting the observer's trouble to select and input one of their range finding points.
Also, in the division photometry of dividing a photographing range into a plurality of regions and making the photometry in each region, there is an effect of remarkably improving the probability of adapting the exposure to a range intended by the observer by applying the information of watching points as described for the weighting of photometry information in each region.
However, generally, the motion of the bulb of human eye includes a saltatory motion which is caused in extracting image features, with its maximum speed reaching 300 degree/second, an accompanying motion, slow and smooth, which occurs for an object moving at less than 30-35 degree/second, and in addition, a fixation minor motion which is irregular, occurring involuntarily to continue to catch an object matter at a central pit. In the still camera or video camera, a display outside the field within a finder may be seen. Thereby, with the eye axis detector as shown in a conventional example, it was difficult to detect correctly the direction of the eye axis or the watching point to an object intended by the observer (or photographer).